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Combinations and Permutations

This is a nice short article on combinations, permutations, and the difference between them. The formulas for the number of ways to select \(k\) objects from \(n\) objects are given in the various cases of ordered or unordered samples, and with or without replacement. The tone is informal and chatty, with some graphics to liven the presentation. The page has links to 10 multiple choice exercises, a link to a combination and permutation calculator, and to a page on Pascal's triangle which has a number of nice graphics.